Voiv. 7, 1921 
PALEONTOLOGY: H. F. OSBORN 
231 
The solubility of CO2 also makes an empirical correction necessary for 
reabsorption of the gas while the volume is undergoing reduction from 
50-5 cc. to a cc. In our apparatus, where S = 50 cc, a = 2 cc, the factor is 
approximately 1.020, the reabsorbed C0 2 being 2 per cent of the total. For 
the less soluble gases reabsorption may be kept negligible. 
No correction for vapor tension is required, since it is practically the 
same at the reading of both m and n. 
For a given gas volume the value of the pressure change (m — n) is 
inversely proportional to that of a. a may accordingly be so chosen that 
for the gas volumes obtained the percentage error in measuring a cc. of 
gas will be of the same order of magnitude as that in measuring the ac- 
companying (m — n) mm. of pressure change. The total volume A of the 
pipette chamber is a matter of convenience, but it is desirable to have it so 
large that the greater part of the dissolved gases shall be extracted. For 
analysis of 1 cc. of blood convenient magnitudes are A = 50, a — 2, 
5 = 2.5. At 20° 1 volume per cent of gas under these conditions gives a 
reading of m — n = 3.9 mm., so that if m — n can be determined within 
0.4 mm. the error is 0.1 cc. of gas per 100 cc. of blood. 
ADAPTIVE RADIATION AND CLASSIFICATION OF THE PRO- 
BOSCIDEAN 
By Henry Fairfield Osborn 
American Museum of Natural History, New York City 
Read before the Academy, April 26, 1921 
In 1900 the author predicted that the source of the mammalian order 
of the Proboscidea would probably be discovered in Africa. In 1901 
Beadnell and Andrews revealed, through the Geological Survey of Egypt, 
the rich fauna of the Fayum, southwest of Cairo, in which were found 
the remains of three proboscidean genera, named by Andrews Mceri- 
therium, Palasomastodon, Phiomia, confirmed by subsequent explora- 
tion and research to be the oldest proboscideans thus far known. Ani- 
mals similar to Mceritkerium and Phiomia have since been reported by 
Pilgrim in southern Asia. These animals are now found to belong re- 
spectively to three distinct lines of the Proboscidea, namely, the moeri- 
theres, the true mastodonts, the long- jawed bunomastodonts, as indicated 
in black on the accompanying diagram. They point, however, to a long 
antecedent origin and radiation. This is part of the evidence for an 
ancient adaptive radiation process by which it now appears that the 
proboscideans, like other hoofed mammals, were broken up into several 
great primary stocks way back in Eocene times, namely : 
An amphibious stock, adapted to rivers and swamps, of limited migration. 
A mastodont stock, adapted to forests and savannas, of wide migration. 
